1. Field of the Invention
The invention is directed to a method for controlling foamed slag in a stainless melt in an electric arc furnace.
2. Related Art
The advantages of a favorably foaming slag in the electric arc furnace (EAF) are well known. WO 2007/087979 A1 can be referenced in this regard.
In electric arc furnace operation, the charge, i.e., primarily scrap and alloys, are melted by the arcs of electrodes while simultaneously forming a slag. Apart from its primary function, i.e., the removal of unwanted constituents from the melt, the slag performs a protective function when brought to a foaming state. In this state, the slag blankets the space between the electrode tips and the surface of the metal and, owing to its poor thermal conductivity, protects the refractory lining of the furnace against the radiant energy of the electric arc.
The foamed slag sharply reduces the intensive radiation of the arc with respect to the wall of the electric furnace and therefore facilitates the input of energy into the metal melt. This substantially prolongs the life of the refractory material of the furnace.
To achieve these benefits, the foamed slag must always be at a predetermined level in the furnace.
EP 637 634 A1 discloses a method for producing a metal melt in which the level of the foamed slag is determined acoustically, namely by detecting a frequency range characteristic of slag foaming. Comparison of the measured sound level with a reference sound level yields reference points for controlling the addition of foaming agents.
WO 2007/009924 A1 also addresses the determination of the level of the foamed slag in an electric arc furnace. In this case, the determination of structure-borne sound is used as measuring technique.